1. Field of the Invention
Exemplary aspects of the present invention generally relate to a transfer device that transfers an image formed on an image bearing member, and an image forming apparatus, such as copiers, facsimile machines, or printers, using the transfer device.
2. Description of the Background Art
Conventionally, image forming apparatuses such as copiers, facsimile machines, or printers include a developing device that develops what is called an electrostatic latent image formed on an image bearing member, for example, a photoreceptor, with toner to form a visible image, also known as a toner image; a transfer device that transfers the toner image onto a transfer member; and a fixing device that fixes the toner image onto the transfer member.
In the case of color image forming apparatuses such as color copiers and color printers capable of producing a color image, the color image forming apparatus is equipped with a plurality of developing devices for different colors, black, cyan, magenta, and yellow, to form toner images of each respective color. After forming the toner images on each of the photoreceptors, the toner images are sequentially and overlappingly transferred onto an intermediate transfer belt while the intermediate transfer belt rotates, thereby forming a composite color toner image on the intermediate transfer belt. Then, the composite color toner image is transferred from the intermediate transfer belt onto a transfer member, for example, a recording medium, and fixed on the recording medium by the fixing device to form a color image on the recording medium as the output.
Conventionally, in the transfer device of the color image forming apparatus, the intermediate transfer belt is wound around a plurality of rollers. Consequently, if such rollers are deformed or are not properly installed, desired parallelism of the intermediate transfer belt between the rollers is not obtained, causing the intermediate transfer belt to drift laterally, that is, in a width direction thereof, as it rotates. As a result, distortion or color drift may occur in a resulting output image, thus degrading imaging quality. Prevention of undesirable drift of the intermediate transfer belt is of critical importance for pursuing high imaging quality.
To address such difficulty, Japanese Unexamined Patent Application No. 2007-178938 (JP-2007-178938-A) proposes a method for preventing drift of the intermediate transfer belt. The method includes a plurality of rollers that rotatably supports the intermediate transfer belt, one of which supports the intermediate transfer belt in an inclined manner. This roller is a so-called steering roller, which is inclined based on the position of an end portion of the intermediate transfer belt as detected by a detector to prevent the intermediate transfer belt from drifting.
In such a method, the position of the intermediate transfer belt in a main scanning direction is regulated by resistance of contact between the surface of the intermediate transfer belt and the steering roller. Thus, the reliability of drift adjustment relies largely on the tension of the belt, which is a key factor for determining the resistance of contact between the surface of the intermediate transfer belt and the steering roller.
Unfortunately, a variety of factors complicate maintenance of the proper tension on the intermediate transfer belt. Such factors include conventional techniques to extend the lifespan of the intermediate transfer belt and the photoreceptors, as described below, as well as methods of improving cleaning performance and even the type of imaging information involved.
When forming a monochrome image in the color image forming apparatus to extend the lifespan of the intermediate transfer belt and the photoreceptors, there is known a method in which the intermediate transfer belt is separated from the photoreceptors of cyan, magenta, and yellow toners.
By contrast, in another known method for extending the lifespan of the intermediate transfer belt and the photoreceptors, all the photoreceptors are separated from the intermediate transfer belt upon completion of an image forming operation. In this configuration, before rotation of the photoreceptors and the intermediate transfer belt is halted, all the photoreceptors are separated from the intermediate transfer belt upon completion of the image forming operation. Accordingly, damage caused by abrasion due to a difference in linear velocities of the photoreceptors and the intermediate transfer belt when stopping rotation of the photoreceptors and the intermediate transfer belt may be prevented.
There are other instances in which the intermediate transfer belt is separated from the photoreceptors. For example, when a lubricating agent is applied to the intermediate transfer belt and/or when the intermediate transfer belt is rotated in reverse for better cleaning, the intermediate transfer belt is separated from the photoreceptors. Typically, the lubricating agent is applied when the image forming apparatus is used for the first time or after replacing the intermediate transfer belt with a new belt.
In order to separate the intermediate transfer belt from the photoreceptors, the rollers that wind and stretch the intermediate transfer belt need to be moved. Unfortunately, moving the rollers causes a path along which the intermediate transfer belt moves to change, thereby changing undesirably the tension of the intermediate transfer belt. As noted, when the tension of the intermediate transfer belt changes undesirably, the resistance of contact between the intermediate transfer belt and the rollers including the steering roller changes, thereby complicating efforts to control the position of the intermediate transfer belt in the main scanning direction.
Furthermore, the belt tension also changes when the image forming apparatus receives image information consisting of both a monochrome and color images. In such a case, the print mode is switched between the monochrome print mode and the color print mode, thus changing the moving direction of the intermediate transfer belt. As a result, the speed of the intermediate transfer belt fluctuates undesirably, causing distortion and/or color drift in the resulting output image.
The tension of the intermediate transfer belt also changes when automatically applying the lubricating agent to the intermediate transfer belt. In order to apply the lubricating agent to the intermediate transfer belt, the intermediate transfer belt is separated from all the photoreceptors while rotating. As a result, the belt tension may be reduced and the belt thus loosened, thereby undesirably contacting other parts of the image forming apparatus and thus getting damaged.
Another difficulty derived from this configuration is that when automatically applying the lubricating agent onto the intermediate transfer belt, the intermediate transfer belt is separated from all photoreceptors from a single point. This separation point does not change even when replacing the intermediate transfer belt or the transfer device or the photoreceptors. In addition, the gap between the intermediate transfer belt and the photoreceptors when the intermediate transfer belt is separated is relatively narrow, complicating replacement of the above mentioned parts and causing the intermediate transfer belt to undesirably come into contact with the photoreceptors and other parts.
In view of the above, JP-2008-233196-A proposes an image forming apparatus equipped with a transfer unit to reduce fluctuation of the tension of the intermediate transfer belt between the monochrome print mode and the color print mode. The transfer unit includes link members serving as a tension adjustment mechanism for the transfer belt. The link members adjust the tension of the transfer belt in conjunction with a plurality of transfer rollers separating from the photoreceptors disposed opposite the transfer rollers.
In the above-described approach, a spring, which urges a tension roller which is one of the rollers around which the intermediate transfer belt is wound, is attached to one end of the link member. The tension roller is urged by the spring against the intermediate transfer belt. By moving the link members, the length of the spring does not change significantly between the monochrome print mode and the color print mode, thereby suppressing fluctuation of the tension of the intermediate transfer belt.
Although advantageous, this configuration has a drawback in that because the tension of the intermediate transfer belt is adjusted by moving the tension roller urged by the spring in accordance with the movement of the color transfer rollers corresponding to the photoreceptor drums, causing the link members to move in conjunction with the movement of the tension roller, significant stress may be applied on the parts used in this operation.
Furthermore, the position of the transfer roller for black is fixed. This means that the transfer roller for black does not separate from the intermediate transfer belt. Yet JP-2008-233196-A does not disclose the automatic application of the lubricating agent while the intermediate transfer belt is separated form all photoreceptor drums and rotated, nor does it disclose how the intermediate transfer belt is prevented from getting damaged when replacing the intermediate transfer belt or the transfer device or the photoreceptors, either.
In view of the above, there is demand for a device capable of minimizing operational load on the intermediate transfer belt and/or adjacent components when the intermediate transfer belt contacts or separates from the photoreceptor drums while preventing fluctuation of the tension of the intermediate transfer belt, thus preventing loosening and drift of the intermediate transfer belt in the main scanning direction.